(1) Field of the Invention
The present invention relates to a proportional spacing display apparatus for displaying characters with the pitches correspondent with types of character on the screen of a display device such as a CRT.
(2) Description of the Prior Art
With a word processor having a document editing function and comprising an image display and a typewriter, for example, the image display generally shows characters with a fixed pitch whereas the typewriter, when the proportional spacing mode is selected, is capable of printing the characters with corresponding widths, which are pleasing to the eye.
This characteristic of the above word processor entails the following disadvantage in use.
When the proportional spacing mode is selected for the typewriter, printed lines include various numbers of characters depending on the types of character. These lines, when shown on the display which provides a constant pitch display, are unjustified at the righthand end which presents a poor appearance. It would be convenient to the operator in preparing a document if the display presents characters in the form in which the characters are printed. However, the above type of word processor is awkward to use since the lines are justified on the typewriter but not on the display.
For such a word processor, what is known as proportional spacing display system has been developed which enables characters to presented on the display with widths correspondent with the types of character. However, this system varies the frequency of a dot clock with the types of character, which requires a very complicated and expensive circuitry.